Brake issue, 84 Carrera

jlr69s · jlr69s's Garage

Hello all. I have been having some brake issues lately and am very stumped as to what the problem is stemming from. When I push the brake pedal in it feels like I 'hit' something and the pedal stops. Definitely not hitting the floor with the pedal but something about half way.

I have replaced all the brake lines, including the pre-bent metal lines, replaced the master cylinder, and had the lines vacuum bled by my shop. Don't think its air in the lines. I rebuilt the calipers a while ago too. The rear brakes seem to be working harder as they are wearing faster than the fronts.

At about half pressure the brakes work fine. While going slow I can push the pedal in till it 'stops' and it feels like Im slowing down in an SUV, cant lock anything up even if I tried. Almost ran into the back of a car this weekend when I needed to stop and just slowed down. Definitely puckered up a bit!

So, do any of you experts have any idea what could be going on? Brake wise its a stock 1984 Carrera 3.2

Oh Haha · 03-08-2010, 04:48 PM

DO NOT DRIVE THE CAR UNTIL YOU GET IT FIXED. Don't take a chance of hurting someone or yourself.
Did you replace the rubber brake lines? If not, do so.

To me, it sounds as if the rears are doing all of the work instead of "assisting" the fronts. I would pull the front wheels and have a helper push the pedal and see if the front pads are coming out to touch the rotor. I suspect they are not.

Also, check your brake lines for any bulging or sponginess as the helper pushes the pedal.

The question is why?

jlr69s · jlr69s's Garage

Brake lines have ALL been replaced. No sponginess in the pedal, it just gets to a point and stops, feels like it actually hits a stop but does not go to the floor (not that bad.) The brakes work fine under normal conditions but in emergency conditions it stops like my old Chevy Silverado. Definitely looks like the rears are doing more of the work...

newms · 03-08-2010, 06:31 PM

Almost sounds like the front pads have glazed. Put in new oem pads and see if it is any better.

jlr69s · jlr69s's Garage

since I noticed the issue a while ago and started to self diagnose I have since changed the front and rear pads when I rebuilt the calipers. The thing that stumps me is the feeling of the pedal hitting 'something' on the down stroke...

pete3799 · pete3799's Garage

Have you pulled up the floor board and checked for an obstruction?

JP911 · JP911's Garage

Have you checked the pedal cluster and all of the linkage between the brake pedal and the brake booster? May be a mechanical issue, not a hydraulic issue.

jlr69s · jlr69s's Garage

Quote:

Originally Posted by JP911

Have you checked the pedal cluster and all of the linkage between the brake pedal and the brake booster? May be a mechanical issue, not a hydraulic issue.

Ill take a closer look at the cluster in the morning. Thanks, I hope its something simple!

uwanna · 07:33 PM

I had an identical symptom on my '80 SC. Tried everything with no luck, till I changed out the master cylinder. Voila! had super brakes once again.
your problem may be something else, but sounds like you've tried everything else!

EDIT: just reread your post and saw you replaced the MC, maybe the new one is defestive. Just guessing.

jimbauman · 03-08-2010, 07:34 PM

Well given that you're from Florida, I bet you'll find that missing Titleist that used to rattle around under the seat...

Did this just start suddenly one day and remain constant, or have the symptoms changed over the period of time we're dealing with here?

JB

jimbauman · 03-08-2010, 07:37 PM

Quote:

Originally Posted by uwanna

EDIT: just reread your post and saw you replaced the MC, maybe the new one is defestive. Just guessing.

defestive: a master cylinder that does NOT like to party....

Oh Haha · 03-09-2010, 03:01 AM

Quote:

Originally Posted by pete3799

Have you pulled up the floor board and checked for an obstruction?

Man, I didn't even give the most simplest of issues a thought. duh

Thanks for pointing out what might be the obvious problem, Pete.

jlr69s · jlr69s's Garage

Jim: LMAO!! I play with Nike balls but regardless, Ill have a look under the floor board and around the cluster/linkage to see if its an obstruction.

Uwanna: I was kind of thinking it was a defective MC too, if all else fails Ill replace it again.

Heading out there right now to have a look and will post any new findings in the next few hours. Thanks for the help everyone!

CCM911 · 03-09-2010, 05:53 AM

Hey, I had the same problem on my 1984 Tagra. Every time I would hit the brakes in the rain, the ass end would slide out. And when I went to the track, I would go through rear pads quicker than the fronts. I needed a new proportioning valve. It s right in the smuggler's box, and will take more time to bleed the system afterwards than to replace. It is a hundred dollars, but then again, do you really want to waste time screwing with the MC again? Here is the link:

Pelican Parts - Product Information: 928-355-305-02-M100

450knotOffice · 450knotOffice's Garage

My two thoughts are:

- Check the pedal cluster for obstructions and worn bushings
- Proportioning valve

jlr69s · jlr69s's Garage

Rear is not locking up, it just seems (by looking at the pads) that they are doing more work than the front. Still think it might be the proportioning valve? Im kind of convinced that somehow there is air in the lines, maybe in the MC itself... Someone PM'ed me about a spare proportioning valve he had, if its a good deal you think I might as well install it or try some more bleeding before spending money?

CCM911 · 03-09-2010, 08:53 AM

Put in the new proportioning valve. If that is not it, then you can bleed some more. If the valve is a good deal, just do it and eliminate one more possible trouble area.

gabenheimer · 03-09-2010, 04:58 PM

Tell us about your rotors. Sounds like you have rebuilt the calipers and changed the pads. Did you check the rotors for run out? Dished or grooved rotors can impact brake feel and cause the pads to glaze. This would make it stop like a Silverado. I can relate, my wife has a Chevy Tahoe and the brakes feel like a wet sponge under hard braking.

In my Carrera I was going insane trying to figure out why I had such a lousy pedal feel under hard braking. Like you, I had new pads, fluid, brake lines, and a new master cylinder. I was just about to change the proportioning valve when I decided to check the rotors. Sure enough, the front rotors looked good but were severely dished. New rotors and pads all around turned my car from a Tahoe into a track star.

Just curious when you replaced the master cylinder did you also replace the booster?

Randy

wildcat077 · wildcat077's Garage

Just a shot in the dark...
I read something about piston orientation when you rebuild the calipers,could that be an issue in your case ?

Phil

jlr69s · jlr69s's Garage

Quote:

Originally Posted by gabenheimer

Tell us about your rotors. Sounds like you have rebuilt the calipers and changed the pads. Did you check the rotors for run out? Dished or grooved rotors can impact brake feel and cause the pads to glaze.

Sure enough, the front rotors looked good but were severely dished. New rotors and pads all around turned my car from a Tahoe into a track star.

Just curious when you replaced the master cylinder did you also replace the booster?

Randy

The rotors look fine, visually. The fronts look pretty new as they are and the rears look like they are worn a bit but nothing that concerns me. Ill have to ask my dad, who had the car before me, when the rears were last replaced. Its probably been a little while but like I said they dont look terrible. A few rotational groves but nothing bad. Unfortunately it wont be until Saturday when I can get under the car again. Just order some parts from Pelican and I will replace the rear pads (needed) and maybe go ahead and do the rotors as well. I will also be bleeding the brake lines at the MC as I have a feeling there is some air in there. Thanks again all and I will post an update by the weekend!